Clacking? Any possibility the injectors are worn? Injectors are only good for so long.

Does the noise get louder if you come to a stop sign and then accelerate?

Use a long screwdriver and listen.

Sorry you can't catch a break with these engines.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k